Grow food, not grass, to fight climate change

Turning a grassy lawn into a vegetable garden can significantly reduce greenhouse gas emissions, according to a new study.

Every kilogram of homegrown vegetables can cut greenhouse gas emissions by 2 kg, a new study finds.
(Photo: MNStudio/Shutterstock)

There are plenty of reasons why it's smart to grow vegetables at home. You have easy access to nutritious local food, your immune system is boosted by soil microbes, and you get an array of health benefits like reduced stress and improved sleep.

Scientists from the University of California Santa Barbara, led by research professor David Cleveland, found that greenhouse gas emissions can be reduced by 2 kilograms for every kilogram of homegrown vegetables, when compared with store-bought vegetables. This is due to several factors, they report, including:

converting a section of grassy lawn into vegetable production.

producing food where it's consumed — people's homes — rather than at centralized farms, reducing the need for transportation.

reusing some household gray water to irrigate vegetables, instead of sending it away to a wastewater treatment plant.

composting food and yard waste in lieu of sending it to a landfill.

The researchers used Santa Barbara County, California, as an example location, calculating that a garden measuring 18.7 square meters (about 200 square feet) could generate half of all vegetables consumed by the average household. For context, the average size of a private lawn in the U.S. is estimated to be about one-fifth of an acre — that's 809 square meters, or 8,712 square feet.

Productive produce

To keep their findings conservative, the study's authors chose mid-range numbers from a wide range of values in existing data, the university explains in a press release. Their estimate of garden productivity is based on 5.72 kg of vegetables per square meter of garden per year, but at a higher yield of 11.44 kg, that same 18.7 square-meter garden could supply 100 percent of a family's vegetables.

Using the 5.72 kg per-garden yield, the researchers extrapolated from Santa Barbara County to the state of California overall. If half of the state's single-family homes grew gardens big enough to supply just 50 percent of their vegetables, they would contribute more than 7.8 percent of the state's greenhouse gas emissions (GHGE) goal, which calls for reducing emissions to 1990 levels by 2020.

And for an individual family, growing 50 percent of their vegetables in a home garden is equivalent to an 11 percent drop in carbon dioxide emissions from driving a car.

"These results suggest that [vegetable gardens] could make an important contribution to household GHGE mitigation, while supplying a portion of an average single-family household's vegetable consumption," the researchers write.

This study breaks new ground for gardening, its authors add, offering the first evidence that homegrown vegetables can significantly help local and state governments meet their targets for reducing greenhouse gas emissions.

"To date, no research has estimated the potential contribution of household vegetable gardens to reduce GHGE and contribute to mitigation targets," they write. "[H]ousehold gardens have been neglected in food and urban policy compared with community gardens, though they likely often comprise a much larger area."

Careful with compost

Household gardens only help the climate if they're well-managed, though. Emissions cuts could be far more modest, the analysis found, if gardeners use mineral fertilizers, till the soil too often, achieve low yields or waste much of their edible harvest. And the way we deal with compost is especially key, the researchers explain.

"There's the potential for home composting to be either positive or negative for the climate," Cleveland says. "It takes a lot of attention to do it right."

If gardeners don't maintain the right moisture and air conditions in a compost bin, the waste can become anaerobic. It may then emit methane and nitrous oxide, two potent greenhouse gases, eroding the other climate benefits of a home garden.

"We found that if household organic waste was exported to landfills that captured methane and burned it to generate electricity, households sending their organic waste to a central facility would reduce greenhouse gas emissions more than composting at home," Cleveland says. "This study shows that in terms of effect on the climate, small things matter. How much attention you pay to the garden matters. How efficiently the vegetables are produced and consumed matters."

Dig for victory

Another perk of home vegetable gardens is that, compared with other ways to combat climate change, they require no new technology or infrastructure, the study's authors point out. That doesn't mean there aren't hurdles, however.

"A major challenge to implementing [home gardens] on a wide scale is motivating household and community members to create and maintain the gardens, and to eat the vegetables they produce," the researchers write.

Luckily, there's a precedent in modern history of people rallying to garden for a greater good: 20th-century victory gardens. The concept began in World War I and expanded during World War II, when victory gardens were widely promoted in the U.S., Great Britain and other Allied nations as a way to limit wartime pressure on food supplies. The U.S. alone had 20 million victory gardens at the height of WWII, and by 1944 they produced about 40 percent of the country's vegetables.

These gardens were grown "as a result of the response at the national, state and local levels to the crisis of war," the study's authors note.

"While the climate crisis is not yet perceived with the same sense of urgency that motivated these war efforts," they add, "this may be rapidly changing."